Add ConvertToBinary to MCExecContext

For ValueRefs that aren't already a DataRef, this converts to a string and then creates a DataRef out of the native bytes of the string.
Change MCU_puturl to use an ExecContext instead of an ExecPoint

An overload still taking the traditional EP has been provided for existing callers.
Change MCNetworkExecPutIntoUrl to no longer use GetEP

Does its thing using an ExecContext instead of an EP now.
Merge remote-tracking branch 'upstream/refactor-syntax_unicode' into refactor-syntax_unicode_puturl

Conflicts:
	engine/src/exec-network.cpp
	engine/src/exec.cpp
Efficiency improvement in string handling
Merge branch 'refactor-syntax_unicode_puturl' into refactor-syntax_unicode